It is generally known for a wheel bearing apparatus which supports a vehicle wheel relative to a suspension apparatus to incorporate a wheel speed detecting apparatus to detect a rotation speed of a vehicle wheel to detect the wheel speed to control the anti-lock braking system (ABS). Such a bearing apparatus generally includes a wheel speed detecting apparatus with a magnetic encoder. The magnetic encoder has magnetic poles alternately arranged along a circumferential direction integrated into a sealing apparatus, arranged between the inner and outer members, to contain rolling elements (balls or rollers). A wheel speed detecting sensor detects the variation in the magnetic poles of the magnetic encoder according to the rotation of the wheel.
The wheel speed sensor is usually mounted on a knuckle after the wheel bearing apparatus has been mounted on the knuckle to form a suspension apparatus. Recently, it has been proposed that a wheel bearing apparatus be incorporated with a wheel speed detecting apparatus where a wheel speed detecting sensor is self-contained within the wheel bearing. This reduces the size of the wheel bearing apparatus as well as eliminates troublesome air gap adjustment between the wheel speed sensor and the magnetic encoder.
An example of a prior art wheel bearing apparatus incorporated with a wheel speed detecting apparatus is known in Japanese Laid-open Patent Publication No. 2003/254985 as shown in FIG. 15. This wheel bearing apparatus incorporated with a wheel speed detecting apparatus includes an outer member 101, forming a stationary member secured on a suspension apparatus (not shown) and an inner member 102, defining a wheel hub 105 and an inner ring 106, inserted into the outer member 101 via double row rolling elements (balls) 103 and 103. The outer member 101 has an integrally formed wheel mounting flange at one end and double row outer raceway surfaces 101a and 101a formed on its inner circumferential surface. The inner member 102 is formed with double row inner raceway surfaces 105a and 106a opposite to the double row outer raceway surfaces 101a and 101a. One (105a) of these double row inner raceway surfaces is formed on the outer circumferential surface of the wheel hub 105. The other surface (106a) is formed on the outer circumferential surface of the inner ring 106. The inner ring 106 is press-fit onto the cylindrical portion 105b and extends axially from the inner raceway surface 105a of the wheel hub 105. Double row rolling elements 103 and 103 are arranged between the outer and inner raceway surfaces 101a and 101a; 105a and 106a, respectively, and are held in position by cages 107 and 107.
The wheel hub 105 has an integrally formed wheel mounting flange 104 to mount a wheel (not shown) and hub bolts 104a to secure the wheel. The hub bolts 104a are rigidly secured on the wheel mount flange 104 and are equidistantly positioned along its periphery. A serration 105c is formed on the inner circumferential surface of the wheel hub 105. A stem portion 111 of an outer joint member 110, forming a constant velocity universal joint (not shown), is inserted into the serration 105c. Seals 108 and 109 are arranged at both ends of the outer member 101 to prevent leakage of grease contained within the bearing as well as ingress of rain water or dusts.
The inboard side seal 109, as shown in an enlarged view of FIG. 16, is fit into the inner circumference at the end of the outer member 101. The seal 109 has a first sealing plate 112 and a second sealing plate 113 having a “L” shaped cross-section. The second sealing plate 113 has a cylindrical portion 113a fit onto the outer circumference of the inner ring 106. A standing portion 113b extends radially outward from the cylindrical portion 113a. A magnetic encoder 114 is adhered, via vulcanized adhesion, on the outer surface of the standing portion 113b. The magnetic encoder 114 is formed of a rubber magnet with N and S magnetic poles alternately arranged along the circumference direction.
The first sealing plate 112 includes a metal core 115 having a substantially “L” shaped cross-section. A sealing member 116, including a side lip 116a, is in sliding contact with the inner side surface of the standing portion 113b of the second sealing plate 113. A pair of radial lips 116b and 116c is in sliding contact with the cylindrical portion 113a of the second sealing plate 113.
An annular sensor holder 119 is mounted on one end of the outer member 101. The annular sensor holder 119 includes a fitting cylinder 117 and a holding member 118 connected to the fitting cylinder 117. The fitting cylinder 117 has an annular configuration with an “L” shaped cross-section. The fitting cylinder 117 includes a cylindrical portion 117a and a flange portion 117b which extends radially inward from the cylindrical portion 117a. 
The holding member 118 is made by synthetic resin molding it to an annular body in which a wheel speed sensor 120 is embedded. The wheel speed sensor 120 is arranged opposite to the magnetic encoder 114, via a predetermined air gap therebetween. The wheel speed sensor 120 includes a magnetic detecting element such as a Hall element, a magnetic resistance element (MR element) etc. changing characteristics in accordance with the flowing direction of magnetic flux, and an IC incorporated with a waveform shaping circuit for shaping the output waveform of the magnetic detecting element.
A labyrinth seal is formed by a small gap 121 by arranging the flange portion 117b of the fitting cylinder 117 opposite to the end surface of the inner ring 106, via the small gap 121. This prevents ingress of foreign matter from outside of the bearing apparatus, such as magnetic powder, into a space between the magnetic encoder 114 and the detecting portion of the wheel speed sensor 120 even before the stem portion 111 of the outer joint member 110 is inserted into the wheel hub 105. The ingress is prevented even though it includes a course where the bearing apparatus is transferred to an assembly line of a manufacturer of automobiles. Accordingly, the reliability of detecting the rotation speed of wheel can be improved.
However, although the wheel bearing apparatus incorporated with a wheel speed detecting apparatus of the prior art has the effects mentioned above, it is impossible to prevent ingress of foreign matter from outside of the bearing apparatus, such as magnetic powder, into the space between the magnetic encoder 114 and the detecting portion of the wheel speed sensor 120 under severe circumstances in real running conditions of the vehicle.